Photoelectric musical instruments and the like



March 10, 1964 E. M. JONES ETAL PHOTOELECTRIC MUSICAL INSTRUMENTS AND THE LIKE 4 Sheets-Sheet 1 Original Filed Aug. 25, 1955 INVENTOR.

EDWARD Mdouss m0 WESLEY Love March 10, 1964 E. M. JONES ETAL 3,124,535

PHOTOELECTRIC MUSICAL INSTRUMENTS AND THE LIKE Original Filed Aug. 25. 1955 4 Sheets-Sheet 2 TONE COLOR SWITCHING P76 f- 75 INVENTOR. Eowmzo M.Jomzs AND WESLEY Love ATTORNEYS.

March 10, 1964 E. M. JONES ETAL 3,124,635

PHOTOELECTRIC MUSICAL INSTRUMENTS AND THE LIKE Original Filed Aug. 25, 1955 4 Sheets-Sheet 4 n r I z 1:4- E E E U 1 t w "T Q1}- 2 1 1. I l I 2 o u I l i 23% J O DU l E a 1 CL 0 V l I I I x L f U PFE'EQEHQHEE ,9l Honsa n I 8 VSWVQ s 2mm a \t} ,8 13mm 3 2mm 2 (Q16. ,1; nolam 3090 g gQQ g2 OHVZVN I w I I I ,z ONLLHVH 8 ENTOR. EDWARD M. as AND WESLEY Love ATTORNEYS.

3,124,635 PHOTOELECTRIC MUSICAL INSTRUMENT AND THE LIKE Edward M. Jones and Wesley Love, Cincinnati, Ohio, gslslignors to D. H. Baldwin Company, a corporation of Original application Aug. 25, 1955, Ser. No. 530,570, new Patent No. 3,023,657, dated Mar. 6, 1962. Divided and this application Mar. 5, 1962, Ser. No. 177,430

8 Claims. (Cl. 84-1.18)

This application is a division of the copending case in the names of the same inventors, Serial No. 530,570, filed August 25, 1955, entitled-Photoelectric Musical Instruments and the Like, which will issue March 6, 1962, as Patent No. 3,023,657.

Photoelectric musical instruments, as hitherto most highly developed in the art (see, for example, U.S. Patent No. 2,576,759 to Edward M. I ones) have made use of a rotating pitch disc to provide the several desired frequencies, a stationary voice disc containing wave form modifying means to provide the several desired timbres,

United States Patent and a shutter mechanism, together with a photocell on one side of the combination and a light source on the other.

Shutter mechanisms have been simplified and perfected (see, for example, US Patent No. 2,506,599 to John F. Jordan), and consist in general of a supporting disc or plate and shutter elements'actuable to cover and uncover simultaneously a plurality of shutter openings for notes in the same or different registers. The note openings are arranged in groups for the various timbres or voices, and these are controlled in turn by door-like shutters adapted to cover or uncover the separate groups.

Such instruments, in the provision of electrical organs, have certain important advantages. Very beautiful tones may be produced since exact control of the wave forms is possible, and these tones may readily be produced in sufficient number to give a highly flexible instrument. Also, the problem of electricalwiring is reduced to a minimum, since the entire output of the instrument may be picked up by one or a small number of photocells, which in turn, can be connected directly to an amplifier. At the same time, they have the disadvantage of requiring mechanical connections between the shutter mechanism and each of the playing keys as well as to each of the stop tabs. Thus there will be within the console a complexity of mechanical transmission elements, which is expensive, takes up room, and impedes servicing.

It has hitherto been suggested that an arrangement might be effected whereby the desired individual tones could be selectively derived by electrical circuit means, thus eliminating or simplifying shutter mechanisms, and doing away with the aforesaid mechanical connections. This would require a separate photocell for each note, and usually each note in each voice, which at the outset is a matter of great expense for equipment. No one has previously suggested any construction for an instrument employing such a system, which is not bulky, unwieldly, and complicated (if the instrument is to. have desirable range and flexibility) as well as expensive.

One of the objects of the present invention is the provision of an instrument which will combine the advantages of both systems while eliminating the disadvantages of each.

It is an object of the invention to provide a mechanically simplified and less expensivephotoelectric instrument.

It is an object of the invention to provide for the derivation of voices at different pitches from the same keys in a photoelectric musicalinstrument.

It is an object of the invention to provide electrical keying systems for photoelectric musical instruments,and

in particular keying systems which will produce either sustained or transient type tones.

These and other. objects of the invention, which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, are accomplished by that construction and arrangement of parts of which certain exemplary embodiments will now be described. Reference is made to the accompanying drawings wherein:

FIG. 1 is a partial plan view of an array of photocells on a common support and having one common electrode.

FIG. 2 is a partial plan view of another photocell array which is electrically similar.

FIG; 3 is a partial plan view of a double photocell array of the same electrical type.

FIG. 4 is a partial plan view of a photocell array of a type in which each cell has a polarizing electrode and two other electrodes, the last mentioned electrodes being common to the several photocells in the array.

FIG. 5 is a partial plan viewof a pair of photocell arrays with cross connections for the simultaneous derivation of tonesof different frequency and'voice in a single keying operation. FIG. 6 is a partial plan View of another form of photocell array.

FIG. 7 is a diagrammatic, exploded view of elements of an exemplary tone and voice generator.

FIG. 8 is a fragmentary diagrammatic showing of a system employing a fixed aperture discand a moving voice disc.

FIG. 9 isa fragmentary diagrammatic showing of a system employing a moving voice disc and a photocell disc only, the pitch discbeing omitted andthe frequency being determined by the placement of individual photocell elements on the photocell disc. 2

FIG. 10 is a diagrammatic showing of a system employing a fixed photocell disc, a fixed voice disc, and a moving pitch disc.

FIG. 11 is a partial circuit diagram showing an arrangement in which the individual notes and the voices are each selected by separate switches.

FIG. 12 is a partial circuit diagram showing an arrangement in which individual note selection is accomplished by the selective-polarization of individual photocell assemblies.

FIG. 13 is a partial circuit diagram showing a system adapted for the securing of controlled tone envelopes.

FIG. 14 is a diagrammatic showingof one form of photocell array suitable for use in a photoelectric musical instrument.

i The improvements upon which various modifications of the invention hereinafter described are based contemplate the use of one or more arrays of photocells on a single support, and a consideration of what is involved in this is first in order. In its simplest form, a photoelectric cell comprises a pair of electrodes with a body of light-sensitive material electrically located between them. The photoelectric cells maybe of two general types. In one such type, theimposition of light on the light-sensitive material will generate an electric current, whichmay be amplified and used as such. Simple keying by means of switches can beemployed with such devices.

In a second type of photoelectric cell the resistivity or impedance of the light-sensitive material varies upon the imposition of light thereon. In this type of device, the effectiveness of the cell depends upon the application thereto of an electric current from external source, i.e.' the cell must be polarized. The variations of theapplied current through changes in resistivity can be converted into useful electrical oscillations. This type ofv photoelectric cell may, if desired, be provided with three electrodes with advantages hereinafter set forth; and the keying for Patented Mar. 10,1964

Q a note selection may be accomplished by switches in the leads of the polarizing electrodes.

The invention herein taught is applicable to both types of photoelectric cells.

The invention herein taught has as another of its bases the concept of a combination between a photocell array on a single support and a series of circuit elements on the same support for connecting or interconnecting the individual photocells and other circuit elements. This combination, on its single support, partakes somewhat of the nature of printed circuitry, and portions of its at least may be made by methods appropriate for printed circuitry.

The provision of a photocell array permits the location of a large number of individual photocells in a very small space, appropriate to the use of pitch discs and voice discs of feasible sizes; and the nature of the photocells themselves is such that they are very thin in the direction normal to the support surface, so that the photocell array, which itself is in the form of a plate, may be approached very closely to such elements as pitch discs and voice discs. The inclusion of circuit elements is also important not only in the elimination of external wiring but also in the confining of the photocell array to a very small area. As a support or base, a very large number of insulating materials may be employed, including such materials as resinous panels, hard rubber panels and the like. Because of the desirability of dimensional stability in an array containing a large number of small individual photocells, glass or other vitreous supports are preferred, but the invention is by no means limited to these.

There are various ways in which metallic elements constituting both the electrodes and the interconnecting circuit elements may be imposed upon a suitable base. This may be done by such known means as electroplating, vacuum-vapor deposition, spraying, or the direct adhesion of a preformed sheet or foil of metal to the base. The metal may be selectively applied only in those areas in which its presence is desired. This may be done by printing, by spraying or evaporating, through a stencil, by the application of a suspension of finely divided metal through a silk screen, and in other ways. Where the metal coating is applied generally, unwanted areas of it may be removed by covering the remaining areas with a resist, chemically etching to remove the metal and afterward dissolving off the resist. Such heat treatments may be applied as are desired to unity or treat the metal coating.

In general, an individual photoelectric cell such as herein contemplated will consist of two or more electrode members formed by portions of the metallic coating aforesaid, spaced laterally on the support, the electrode elements being interconnected by a thin layer of the light-sensitive material. As known in the art, the light-sensitive material may consist of or comprise various metals of which selenium is an example, or various salts of which lead sulphide is an example. The light-sensitive layer may be applied in various ways as by spraying, fusion, vacuum-vapor deposition and the like. Beyond What is set forth in the appended claims, the specific nature of the photocells and of the light-sensitive material does not form a limitation on this invention. To complete an exemplary disclosure, reference is hereby made to an article on page 818 of Nature for June 14, 1947, volume 159, entitled Lead Sulphide Photo Conductive Cells by L. Sosnowski et al., and to an article beginning on page 115 of Journal of Scientific Instruments, volume 4, 1927, entitled The Formation of Films of Lead Sulphide on Glass Surfaces by H. L. Smith.

A structure comprising a support with spaced metallic electrodes thereon may be completed as a photoelectric cell by imposing a layer of photoelectric substance, e.g. lead sulphide, on the support in such a way as to overlap and interconnect the electrodes in a selected area. The metallic elements forming the electrodes and interconnections may themselves be applied in several increments if desired. This is especially valuable in instances where one electric conductor must cross another without making electrical contact with it. For example, it is possible to impose a conductive element on a glass or other base surface, then to coat the portion of the conductor at which the cross-over is to be effected with a thin layer of insulative substance, for example, a resin, and then to impose a second conductor which will cross the first in the said area, thus avoiding direct electrical contact between the conductors. In some of the structures hereinafter described, cross-overs are necessary, and they can be effected in this fashion, although where the circuitry will permit, cross-overs are to be avoided by reason of the added expense.

In photoelectric organs, the pitch discs and voice discs are usually so formed that the pitch and voice representations thereon are quite small and quite close together. For example, a pitch disc may be formed with a series of concentric pitch representations each such representation being, say, not more than A; of an inch wide in the radial direction, the spaces between the representations being of the same or a lesser dimension. The voice representations on the coacting voice disc will be similarly placed and sized. These dimensions do not constitute a limitation on the invention, but are given as an illustration of the fact that in the preferred form of an electrical musical instrument of this type the photocell array will consist of a large number of individual photoelectric cells each of which is quite small in area, the cells being quite closely spaced. Certain aspects of the invention are not confined to the use of voice discs or pitch discs as will hereinafter be explained; and indeed the photocell array to which the invention pertains may be used with film representations of voice or frequency indicia, with rotating cylinders and the like.

It has been found that a large number of very small photoelectric cells may be brought together on a single support even to the extent of having one or more common electrodes on the said support; and that the individual photocells can operate independently of each other and without mutual electrical interference providing each such cell is isolated by an electrode element adequately as hereinafter described. One way in which this may be accomplished is illustrated in FIG. 1 and where 1 is, for example, a portion of a glass base. An electrode 2 is deposited thereon having substantially radially arranged portions la and circumferentially arranged portions 21) so that the electrode has a serpentine form. The electrode may be provided with a contact element 3 near the edge of the base. Other electrodes are shown as at 4, 5, etc. each comprising a circumferentially arranged electrode portion 4a or 5:1 lying between adjacent circumferentially arranged portions of the electrode 2. A stripe or deposit 6 of light-sensitive material overlies and interconnects the electrode elements. Each pair of adjacent circumferential portions of the electrode 2 defines a photoelectric cell; and it will be seen that the cells are completely contiguous, while each cell is margined on three sides by the electrode 2. The array of cells extends radially of the base 1; the number of individual cells in the array may be sufficient to encompass the frequency range of the instrument in a given voice; and the support may bear other arrays of photocells for other voices. Each of the electrodes 4, 5 etc. may be provided with a contact element 7 or 8 at or near the edge of the support, and to which circuit connections may be made.

In FIG. 2 there is illustrated a common electrode having a substantially radially arranged body 9 and a plurality of circumferentially arranged, spaced branches 10, 11 etc. Additional electrodes 12, 13 etc. are provided, having circumferentially arranged branches lying between the branches 10, 11 etc. of the first mentioned electrode. A coating of light-sensitive material 14 completes the photocells. The electrodes 12, 13 etc. may be provided with contacts 15, 16 etc. near the edge of the support 17.

The branches of the first mentioned electrode define the individual cells, which are adequately isolated thereby.

In FIG. 3 a somewhat expanded arrangement is shown enabling the provision of two photocell arrays in a confined space. Here on the base 18 a common electrode I is provided having a radially arranged body 19 and circumferentially arranged branches 20, 21 etc. extending from both sides of the body. At each side of the body isprovided a series of electrodes 22, 23 etc. and 24, 25 etc. coacting with respective pairs of the branches as shown. Coatings of light-sensitive substance 26, 27 complete the two arrays. The common electrode has a contact element 28 adjacent the edge of the support; and the coacting electrodes have similar contact elements 29, 36) etc.

For certain purposes. hereinafter set forth, it is desirable that each photocell have three electrodes. One way of accomplishing this is shown in FIG. 4. One common electrode has a substantially radial body 31 and circumferentially arranged branches 32, 33 etc. Another common electrode has a substantially radially arranged body 34 and circumferentially arranged branches 35, 36 etc. The branches 35, 36 of the second common electrode cross the portion 31 of the first common electrode and must be kept out of electrical contact therewith. To this end the first common electrode has its substantially radial portion covered with a coating 37 of insulating substance prior to the imposition of the second common electrode. The coacting electrodes 38, 39 etc. have branches lying respectively between a branch of the first and a' branch of the second common electrode as illustrated. The individual cells are completed by the imposition of a light-sensitive layer 40 on the support 41; and each individual cell is defined by a branch of'the first and an adjacent branch of the second common electrode. Contact elements may be provided as at 42, 43 and 44.

Yet another such arrangement is illustrated in FIG. 5. On one side of the array there is a common electrode having a substantially radially arranged body 45 and circumferentially arranged branches 46, 47 etc. At the opposite side of the array there is another commonelectrode having a substantially radially arranged body 48 and circumferentially arranged branches 49, 50-etc. The branches of the two common electrodes extend toward each other inintermeshing spaced relationship; and the coacting electrodes consist in circumferentially arranged portions 51, 52 etc. These portions cross the body 45 of the first common electrode and are insulated therefrom by the layer 53. The photocell array is completed by the layer 54 of light-sensitive substance.

In this figure, a second photocell array is generally indicated at B coacting with a first photocell array A.

These arrays may be thought of as for different voices,

and there will therefore be cross connections between the coacting electrodes of each. The second array does not need to be specifically described since it is substantially like the first; but the cross connections are indicated at 55, 56 etc., and will comprise a portion of the circuitry hereinabove mentioned. The common electrodes have contact members 57, 58, 59 and 600m the base'61 and can be used in connection with switching means for voice selection. The coacting electrodes of the several arrays are connected in series as indicated and are provided with contacts 62. The cross connections 55, 56- etc. can be at the same pitch level or at different pitch levels, as for example where it is desired to couple an 8 foot'voice to a 4 foot voice or the like.

An exemplary arrangement for a photoelectric organ is illustrated diagrammatically and in an exploded fashion in FIG. 7. The arrangement comprises a light source 63 which will be provided with areflector 64. More than one light source may be employed if desired. The light from the reflector first passes through a pitch disc 65. This disc will be rotated at a constant selected speed. It willbear circumferentially arranged pitch indicia, usuthe several voice representations.

ally but not necessarily in theform of light'slits or clear areas 66 in an otherwise opaque ground. The pitch disc will be driven, and means for this purpose are diagrammatically illustrated in FIG. 7 as a pulley 67 and belt 68, though in actual practice it will usually be found preferable to attach a laminated armature to the periphery of the pitch disc and drive it by electro-magnetic means as illustrated and described in the aforesaid US. patent to Jones, No. 2,576,759.

The voicedisc 69 bears. on its. surface circumferentiall'y arranged voice patterns 70. These patterns are repetitive circumferentially and are characterized by variations (either in width or in density) characteristic ofthe harmonic content of some particular desired voice. Since the voice disc'is stationary, there is no point in continuing the voice representations 70 for any given timbre beyond an area overlying a particular photocell array. In other words, the voice disc may be divided into segmental areas for different voices.

Finally the assembly comprises the support 71 containing a plurality of photocell arrays designated in FIG. 7

at C, D and E, the general nature of which will be clear from the foregoing explanation. An arrangement is shown whereby the coacting electrodes heretofore described act as the polarizing electrodes and are connected through individual switches 72, 73 etc. to a bus 74 containing a battery or other source of polarizing potential 75. This arrangement is used for note or frequency selection by the operator in accordance with the requirements of a musical composition, the switches 72, 73 being connected to the playing keys of the instrument.

The several arrays of photocells C, D and B may be connected through a switch arrangement 76 to a bus 77 which in turn is connected to an amplifier and loud speaker system. Thus there has been shown in FIG. 7

:the essentials of one form of photoelectric musical instrument providing for the playing of a plurality of notes in selective voices.

In each array in FIGS. 7 and 10 the coating of lightsensitive substance 78 can be arranged so as to be equal to or a multiple of the distance on centers of the light slits 66 in the several rows on the pitch disc or else the same effect can be secured by masking. The masking may be done by the'voicing representations on the voice disc as will be readily understood. The pitch disc breaks up the incident light into traveling beams which scan In this Way the light incident on any one photocell in an array will vary in accordance with a desired fundamental frequency and a preselected number and amplitude of harmonics related to the fundamental.

Other arrangements are possible. For example, as shown in FIG.. 8 aphotocell array'F on a fixed support 79 may be employed in connection with a stationary pitch disc 80 and a rotating voice disc 81. In this instance the voicing representations 82 on the voice disc will be circumferentially continuous; but the pitch disc may be divided up into segmental areas with the light slits differently spaced circumferentially in such segmental areas, 7

A still simpler construction is illustrated in FIGS. 6

and 9. This construction, in addition to the light'source and reflector, employs a fixed disc or support 83 containing arrays of photocells, and a moving voice disc 84. The voice disc has continuous circumferentially arranged wave form representations 85. In this form of structure the areas of light-sensitive material 86 are each arranged radially, and are so narrow in the circumferential direction that they have the effect of scanning the voice representations on the voice disc 84 so as too provide electrical vibrations characterized by a desired fundamental frequency and a harmonic content, the kind and amplitude of which is determinedby the Voice or wave form representations in the series 85. It is possible in this structure to multiply circu'mferentially the number of areas of light-sensitive material 86 in the various circumferential series so as to attain greater volume, the said areas being interspaced from each other a circumferential distance equal to or a multiple of the length of individual wave form representations on the voice disc.

111 FIG. 6 there is shown a three-electrode system comprising a common electrode having a substantially radially arranged body 87, and circumferentially arrange branches 88, 89 etc., the branches contacting the areas of lightsensitive material near one end in each row. Another electrode such as 90 or 91 is arranged to contact the other ends of the areas of light-sensitive material as shown, while a third electrode such as 92 or 93 traverses the centers of these areas. What is in efiiect a two-electrode system is shown in FIG. 9 where a common electrode has a radially arranged body 94 and branches 95, 96 etc. The centers of the various areas of light-sensitive material in each circumferential band is traversed by a separate electrode such as 97 or 98.

The structure just described has the advantage of mechanical simplicity; but it will be evident that a continuous circumferential voicing representation must be provided for each voice in each frequency throughout the range of the instrument. If the instrument has a wide range of frequencies and a wide range of voices, this may lead to the use of large voice discs and photocell assemblies or to a multiplication of these elements.

By means such as have been disclosed, however, it is readily possible selectively to generate electrical vibrations which are characterized by a fundamental frequency and a high content of harmonics of wide range and amplitude, and then secure different voices by selective filtration of the vibrations in ways known to the art. Thus a comparatively simple mechanical photoelectric assembly may be employed which can be, but is not necessarily the structure of FIGS. 6 and 9. In all of the structures thus far described the nature of the vibrations produced as to their harmonic content will of course be determined by the voicing representations on the voice disc. An analytic type instrument in which voice differentiation is secured through selective filtration or by means of formant circuits, can be arranged to generate but a single type of wave form rich in the harmonics adjacent the fundamental; but it can also be arranged to generate two or more types of wave form suitable for selective filtration with or without combination. Thus a wave form may be generated which is rich in the even order harmonics and weak in the odd order, and another wave form may be generated which is rich in the odd order harmonics, the latter being especially adapted for modification to secure woodwind tones. The selection of different voices may be accomplished in all of the modifications herein discussed either by appropriate circuitry containing switches, or by door-like shutters (such as those shown in the Jordan Patent 2,506,599 noted above) adapted selectively to cover and uncover whole arrays of photocells for different voices. But it will have been noted that in the structures herein taught, note selection is accomplished by circuitry including key switches, thus eliminating the problem of individual note shutters and their mechanical connections to playing keys.

The pitch discs and voice discs employed are preferably though not necessarily reproduced photographically from master negatives. The master negatives may be made by methods and apparatus taught in the copending application of Jones, Serial No. 135,912, filed December 30, 1949, now Patent 2,839,960, issued June 24, 1958, and

.entitled Electronic Synchronizing System for Producing Pitch Discs and the Like. As has been understood, the

various fundamentals of the notes of the tempered scale can be closely approximated by series of whole numbers which are not excessively large.

In other words, it is possible to divide any given circle into a series of equal divisions which when the circle is rotated at a fixed speed will give a desired fundamental frequency, and to do this throughout the range of the tempered scale with entire auditory satisfaction both as to the relationship of the fundamental frequencies and the relationship of the harmonic frequencies pertaining thereto. The principle applies to the formation of voice discs as well as pitch discs. In a voice disc each circular division will contain a wave form representation, i.e. variations either in width or density representative of the harmonic content of the desired voice.

Voices can be attained in the practice of the invention by configuring the individual photocells (cg. varying the effective width of the areas of light-sensitive substance between spaced electrodes which are themselves configured for the purpose). In this case a rotating pitch disc may be used to scan the photocells in each array, and the voice discs as such may be omitted.

However, more accurate control can be accomplished by the use of voice discs as set forth above. The preferred form of electric organ employing the principles of this invention, is that shown in FIG. 7, employing a rotating pitch disc, a fixed voice disc and a fixed support or supports containing the various photocell arrays. Very beautiful, individual voices can be secured in such a system from carefully made voice discs; the voice discs may be divided up into segments each producing a different voice at the same frequency; the arrays of photocells may be similarly divided and placed to coact with the voicing representations on the voice disc; crosscoupling means may be provided on the support or supports for the photocell arrays; and an instrument of great flexibility and range may be produced with a single mechanical assembly such as is diagramed in FIG. 7 without mechanical connection to the keys and without an uneconomical complexity of external circuitry. An arrangement of photocell arrays for the swell manual and pedal clavier of such an instrument is diagramed in FIG. 14. The photocell arrays are indicated at G, H, I, etc. It is believed that the figure will be clear to the skilled worker in the light of the legends thereon. He will understand that another assembly of arrays of photocells can be provided for the notes and voices of the great manual in a two-manual instrument. It is possible, of course, to provide any given instrument with a plurality of the mechanical assemblies diagramed in FIG. 7 for the same or different manuals; and where a plurality of such as semblies is provided, it is possible to attain choral effects by slightly detuning them.

The selection of voices in instruments of this class may be accomplished in various ways. As indicated above, door-like shutters may be provided for separate photocell arrays. Separate light sources could be provided for illuminating the wave patterns of each separate voice. Where cross-coupling is not practiced adjacent the photo cell arrays, their leads could be brought through a plurality of switches beneath each key to separate headers, the outputs of which could be selected through appropriate switches. But it is simpler to provide for the selection of voices through one or more switch means for each photocell array as hereinafter illustrated.

In a system in which photovoltaic cells are employed note selection may be accomplished through key switches alone. Where the photocells are of the photo-resistive type, either note selection or voice selection may be accomplished through switches controlling the polarization of the individual cells. FIG. 11 is a partial circuit diagram showing portions of two arrays of photocells indicated at J and K. These cells are of the two-electrode type heretofore described, for example, in connection with FIGS. 1, 2 and 3. A source of polarizing potential is shown at 99, one side of which is grounded as at 100 and the other of which is connected to a bus 101. A branch lead from this bus is connected to the common electrode of the array I through a transient-reducing resistor 1tl2 and a voice selector switch 103 (normally from the bus 101 is connected to the common electrode of the array K through a resistor 105 and a voice selector switch 106. This circuit may also have a similar capacitor 10 7. The coacting electrodes of the photocell array are shown as cross-coupled and as having leads 10-8 and 109. These leads are connected toa bus respectively through switches 111 and 112. Theseswitches may be thought of as connected with the playing keys of the instrument, and are preferably though not necessarily of the gradual-contact type, such as those describedin US. Patent 2,215,124 to Kock and Jordan. Such switches eliminate an unpleasantly abrupt onset of the tones. Each of the leads 108 and 109 may contain a capacitor 113 or 114 bypassed to ground by resistances 115 and 116 or 117 and 118. The purpose of these networks is to filter'out the direct current component of the signal, since the alternating current component is that desired for amplification. The bus 110.is connected to an amplifier 11!) which in turn is connected to a loud speakersystem 120. If desired, filter means 121 may be connected in the bus 110 for tone modification.

Photocell arrays in which the individual cells comprise three electrodes have hereinabove been described as for example in connection with FIGS. 4, 5, 6 and 10'. Such cells have a distinct advantage in that they are adapted to be connected to a push-pull amplifier or its equivalent in such a way as to cancel the. direct currentsignal components, rendering unnecessary the use of filter networks for the purpose as described above, and making possible a different keying system as will later be described. FIG. 12 shows partially and diagrammatically a circuit arrangement employing such cells, while FIG. 10 shows one arrangement of pitch disc and voice disc in connection therewith. In this modification polarization is accomplished through the key switches. Two arrays of photocells are partially indicated at L and M. As before, these may be arrays for difierent voice timbres or for voices of different frequencies or footage values, or both. A source of polarizing potential 122 having one side grounded as at 123 is connected to a bus 124. A branch from this bus passes through a key switch 125 and a transient-reducing resistor 126 to the coacting or intermediate electrodes of interconnected photocells of each array. Another branch passes through a key switch 127 and resistor 128 to another interconnected group of photocells, and so on. The common electrodes of the array M are brought out and connected through a gang potentiometer arrangement 129 to the leads of a balanced amplifier 130 as shown. By using wave forms on the voice disc that are of opposite polarity for the two halves of the three electrode photocells as shown at 70 and 70a in FIG. 10, the signals at the two inputs of the amplifier add whereas the D.-C. or transient components cancel. Instead of a vacuum tube push-pull or difierence amplifier, it is sufficient to use a center-tapped transformer the secondary of which is connected to an amplifier whose first stages at least are single-ended. All of these are intended to be comprised in the term balanced amplifier. A transformer has the advantage of having less input resistance to D.-C., causing less trouble with spurious polarizing voltages being built up across those photocells which are not used at a particular moment. Similarly, the two common electrodes of the array L may be connected to the same leads through a gang potentiometer 131. The amplifier is connected to a loud speaker system 1132. The key switches again may be but need not be of the gradual contact type; and the key switch leads may be provided with transient-rcducing networks 133 and 134.

The circuitry of FIGS 11 and 12 will provide an instrument giving sustained or organ-type tones. Nevertheless, with suitable mechanisms connected with the key switches, it is possible to produce tones of a percussive character, for example, tones of which the initial loudness is dependent upon the key velocity, the tones decaying at a gradual rate. Various mechanisms for this purpose are known in the art andreference is made here to U.S. Patent 2,095,707 to Kucher, to Patent 2,482,548 to Kerkhof, and to Patent 2,302,457 to Midgley et al.

In FIG. 13 there is illustrated a system for the production of percussive, transient or similar type tones, this being a system in which the polarizing voltage of the photoelectric cells is applied through key switches, while the tone signals are selected through stop switches. A source of polarizing potential 135 has two leads 136 and 137. A key switch is indicated at 138 provided. with a resist-or 139. The switch has been shown as a single-pole, double-throw switch. This may be connected with a playing key in various fashions as hereinafter explained. The blade of the switch is connected through the resistor 139 to a lead 1401 to the coact-ing terminal of a photocell 1141 in an array N. Other arrays are indicated in the figure at O and P, and these may be cross-coupled to the first as shown. The common electrodes of the photocells in the array N are connected through a double switch pole,

double-throw 142 or through a potentiometer to the leads of a push pull amplifier 143 feeding a loud speaker 144.

Between the lead and the lead 136 is connected a capacitor 145 bypassed by a resistance 146. During the time the switch 138 makes contact with the lead 137 a charge is applied to the capacitor 145. When this contact is broken, the capacitor 145 is disconnected from the source 135 and discharges, polarizing the photocell 1141 with a potential which is not constant but declines at the rate of discharge of the capacitor, producing a percussivetype tone envelope. The rate of decay or decline of the polarizing potential can be controlled by the size ofthe capacitor and the value of the resistor 146.

The switch 138 may be actuated by the key in various ways. If, upon depression of the key, the switch 138 makes contact with the lead 137 and retains that contact until the key is released, the tone produced will. remain at constant loudness until the key is released, at which time an exponential decay will occur. The effect will be that of organ tones excepting that if the keys are played staccafo, the exponential decay will become apparent, giving a harp-like eflect, or effects similar to plucked strings,

struck bars, etc. If, on the other hand, upon depression of the key the switch makes momentary contact with the lead 137 and then breaks this contact, the exponential decay will occur immediately upon the full depression of the key, giving piano-like eifects. If a mechanism is employed to cause the duration of the contact effected by the switch 138 with the lead 137 to be roughtly proportional to the key velocity, then the loudness of the tone is under the control of the perfomer, or a circuit as in the Kerkhof patent could be used to control loudness.

If, upon depression of the key, the switch 138 first effects contact with the lead 137 and then with the lead 136 when the key is released, the effect will be that of causing the tone to die out more rapidly, simulating the action of the damper in a piano.

Modifications may be made in the invention without departing from the spirit of it. Having thus described the invention in certain exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. In a photoelectric musical instrument, a photocell array on an insulative support, said array comprising a plurality of photocells each with three electrodes formed as metallic coatings on said support, and interconnected by photosensitive material, each photocell comprising an intermediate electrode and outer electrodes, means moving with respect to said insulative support to subject the individual photocells to rays of light productive of electrical vibrations at musical frequencies, selective means for applying polarizing potential to the intermediate electrodes, and means for connecting the outer electrodes of 1 I each photocell with an amplifier system of balanced type, wherein the direct current components in the said outer electrodes neutralize each other, leaving the alternating current outputs for amplication.

2. In a photoelectric musical instrument, a photocell array comprising an insulative support and a series of electrodes in the form of metallic coatings on said support, said electrodes arranged with substantially parallel portions in groups to form the electrodes of contiguous photocells, said electrode portions extending substantially parallel in each said group, and each said group having a plurality of coatings of photoelectric material interconmeeting said electrodes but spaced on said support in the direction of the length of said parallel portions of said electrodes.

3. The structure claimed in claim 1 wherein said photocell array comprises two common electrodes with interdigitating parallel branches, with an additional parallel electrode interposed between each adjacent pair of said branches.

4. The structure claimed in claim 2 wherein one at least of the parallel electrode portions in each group is connected to a common electrical lead on said support.

5. In a photoelectric musical instrument having a light source, the combination of a rotating pitch disc and a stationary voice disc, the pitch disc having concentric divided areas suitable for the production of desired frequencies, and the voice disc having voicing representations also arranged circumferentially but in different, spaced, radial groups, and a plurality of arrays of photocells, one for each radial voice disc group, each said photocell comprising three electrodes in the form of metallic coatings on supporting means, and having substantially parallel circumferentially arranged interdigitated portions, and substantially radially arranged coatings of photosensitive material interconnecting the said parallel pontions of each array, means for connecting photocellsof each array to balanced amplifier means, and means for selectively polarizing the photocells of the arrays.

6. The structure claimed in claim 5 wherein the last mentioned means include tone envelope control means.

7. The structure claimed in claim 5 wherein the three electrodes of each photocell consist of two outer electrodes and one intermediate electrode, wherein the polarizing means is connected to the intermediate electrode, and wherein the means for connecting the said photocells to a balanced amplifier comprise respective connections between theputer electrodes and the ends of a winding of a center-tapped transformer.

8. The structure claimed in claim 2 wherein each group comprises an intermediate electrode and outer electrodes, means moving with respect to said insulative support to subject individual groups to rays of light moving with respect thereto, selective means for applying polarizing potential to the intermediate electrode-s, and means for connecting the outer electrodes of each group with an amplifier system of balanced type, wherein the direct current components in the said outer electrodes neutralize each other, leaving the alternating current outputs for amplification.

No references cited. 

1. IN A PHOTOELECTRIC MUSICAL INSTRUMENT, A PHOTOCELL ARRAY ON AN INSULATIVE SUPPORT, SAID ARRAY COMPRISING A PLURALITY OF PHOTOCELLS EACH WITH THREE ELECTRODES FORMED AS METALLIC COATINGS ON SAID SUPPORT, THE INTERCONNECTED BY PHOTOSENSITIVE MATERIAL, EACH PHOTOCELL COMPRISING AN INTERMEDIATE ELECTRODE AND OUTER ELECTRODES, MEANS MOVING WITH RESPECT TO SAID INSULATIVE SUPPORT TO SUBJECT THE INDIVIDUAL PHOTOCELLS TO RAYS OF LIGHT PRODUCTIVE OF ELECTRICAL VIBRATIONS AT MUSICAL FREQUENCIES, SELECTIVE MEANS FOR APPLYING POLARIZING POTENTIAL TO THE INTERMEDIATE ELECTRODES, AND MEANS FOR CONNECTING THE OUTER ELECTRODES OF EACH PHOTOCELL WITH AN AMPLIFIER SYSTEM OF BALANCED TYPE, WHEREIN THE DIRECT CURRENT COMPONENTS IN THE SAID OUTER 